In bag-shaped beverage containers having a membrane seal which is to be pierced by a pointed straw, such as CAPRI SUN.RTM., there is a problem of providing a sufficiently strong seal to withstand the rigors of shipping while still making the seal sufficiently easy for the consumer to pierce with a straw. In addition, it is often desired to provide a readily observable indication of whether or not the opening system of the beverage container has been tampered with.
In the prior art, an opening system has been used which includes a simple membrane seal on an inside surface of one barrier wall of a bag-shaped container. The membrane seal is sealed up to the edges of the straw hole in the barrier wall near a top of the container. Such a membrane seal is disclosed in U.S. Pat. No. 5,425,583 (Wild). While such a membrane seal is mostly satisfactory, it does not provide evidence of tampering as the membrane seal can be easily ruptured. The problem of tamper-evidency would be further exacerbated if the membrane seal did not extend up to the edges of the straw hole such that a pocket is created between the barrier wall and the membrane seal.
Another opening system for a beverage bag having a portion which can be easily pierced by a straw is disclosed in U.S. Pat. No. 4,762,514 (Yoshida). The bag is made from a pair of laminar panels, with each panel comprising an inner foil layer and an outer reinforcing plastic layer bonded over the inner layer. This outer layer has a high piercing strength and high rigidity. In order to make piercing of the outer layer very easy, a number of radially extending linear cuts in the form of a starburst are formed therein. However, no breakage occurs in the outer layer so there is no tamper evidence when this outer layer is pierced.